Alternating-current motor starting system



Sept. 2, 1941. F. AULD ALTERNATING-CURRENT MOTOR STARTING SYSTEM Filed March 31, 1958 4 Sheets-Sheet 2 WITNESSES: 5.247%

ATTORNEY v effecting the automatic current motors are Patented Sept. 2, 1941 ALTERNATING-C STARTIN Frederick Auld, Charleston, .Westinghouse Electric '8;

Dan]. East Pittsburgh,

Pennsylvania URRENT MOTOR G SYSTEM W. Va., assignor to Manufacturing Com- Pa., in corporation of Application March 31, 1938, Serial No. 199,234 20 Claims. v(Cl. 172-289) My invention relates to tems, more particularly to systems of'control for starting of alternating current motors.

Automatic starting systems for alternating well known. Such known starting schemes, or systems, dependeither on time or onthe current'in the motor windings to control the starting of .the motor.

If the alternating current motor is a synchronous motor, the frequency of the current in the field winding may be utilized to control the instant of application of the direct current excitation to the field winding. With induction motors, the frequency in the secondary winding may also be used. In general, some current characteristic of the current in the armature, field, primary, secondary, or damper windings can be used. The best known of these schemes is the field frequency scheme. v

With a time limit system of control some sort of timing devices are used which allows. definite time to elapse between the application bf the voltage to the primary windings and the establishment of the running For a synchronous motor secondary resistance or both, may ;be controlled by the timing device, or devices.

The use of a time limit control may'for'most motor loads be too slow, thus requiring the motor to run with its starting circuits energized too long. If the time limit is selected shorter to provide for more rapid starting then it may happen, when the motor is heavily loaded,- that heavy surges are produced on the supply and the motor and the load driven thereby may be subjected to shocks during starting. With a field frequency scheme, if the load is heavy, the motor may fail to come up to full speed.

One object of my invention is the provision of a starting scheme for an alternating current motor that partakes of the merits of both the time limit scheme and the current scheme without being subject to the disadvantages of either of the schemes' A broad object of my invention is to utilize a given number of revolutions made by a motor, after the instant of its energization, to control the starting of a motor.

A more specific object of my invention is to control the transfer of a motor from its startcircuits for the motor. the application of the electric control sysvention by no means exhaustive but is merely a study of the following in conjunction with specification when taken the accompanying drawings,

- in which:

Figure 1 is a diagrammatic showing of my invention as applied to a synchronous motor started on full voltage;

Fig. 2 is a sectional view taken along line II-II of Fig. 3 of a revolution counting mechanism constituting part of my invention;

Fig. 3 is a front view of the subject matter shown in-Fig. 2;

Fig. 4 is a side view of one of the mercoid switches operated by the revolution counting device shown in Figs. 2 and 3;

Fig. 5 is a diagrammatic showing of my invention as applied to a low-voltage starting schemefor a synchronous motor;

Fig. 6 is a graphic presentation of hypothetical starting characteristics of a motor, to aid in explaining the speed is 300 R. P. M., or 5 R.

advantages of my invention; and

Fig. 7 is a diagrammatic showing of my invention as applied to an induction motor.

Before describing the details of my invention, some general theoretic explanations and an analysis of a starting cycle of a ful. Let it be assumed that a 600 R. P. M. synchronous motor is to be started, that is, brought up to synchronous speed.

In Fig. 7, I have plotted revolutions per minute against time in seconds using accelerating periods of 10, 20, 30, and 40 seconds. For simlet it be assumed the motor rotor will ac- OH, and OI are this assumption will have no unon the principle involved. I

the 10 second period, the average P. S. and the total number of revolutions while the motor accel- As will appear hereinafter, any.

erates to 600 R. P. M., the full speed, is times or'50 revolutions.

From similar calculations, it is apparent that the total number of revolutions made during each of the 20, 30, and 40 second periods is 100, 150, and 200, revolutions, respectively. Now the number of revolutions made during any accelerating period is proportional to the areas ABF, ACG, ADH, etc. In fact if the time be expressed in minutes then the area is equal to the number of revolutions being the product of average revolutions per minute and the time.

The field frequency starting scheme, or for that matter, any current responsive scheme uses revolutions per minute only, whereas any time limit starting scheme uses time only. By using the combination of time and revolutions per minute, I get the useful characteristics of both starting methods.

Let me assume I know definitely that a motor, connected to a given load, will accelerate in exactly 10 seconds, With a time limit. starting scheme I could set the devices for 10 seconds and at the expiration of that time the rotor will have acquired a maximum speed and, considering a synchronous motor, the field excitation is automatically applied. This would be ideal. But as a matter of fact, no one ever knows the exact time required for each acceleration. Therefore, in order to make sure that the rotor may have sufiicient time to reach maximum speed, the procedure is usual to a longer period than will be required, as for instance 20 seconds. But suppose the rotor does set the control relay for I motor.

actually come up to full speed in 10 seconds, then the motor, though up to speed, must continue to operate on the damper windings for an additional 10 seconds.

With my system of control if the control means, including a revolution counter, is set for 100 revolutions, which corresponds to 20 seconds on Fig. 7, the rotor would have made 50 revolutions while coming up to speed. The rotor is now operating at 600 revolutions per minute and the time required to make the additional 50 revolutions is 5 seconds so that the control, or transfer operations, as the application of the field, occurs in seconds instead of seconds.

In like manner, it will be apparent that had the setting been made for 150 revolutions, the field would have been applied in 20 seconds and with a 200 revolution setting in seconds assuming in each case that the rotor actually comes up to full speed in 10 seconds. It is now apparent that any variation from the straight line acceleration which I assumed originally and which is graphically represented in Fig. 7 would only increase or decrease slightly the number of revolutions made during acceleration, thus decreasing or increasing slightly the number of revolutions made after the accelerating period.

From the foregoing discussion, it is apparent that my starting scheme will to some extent automatically adjust the time to suit the actual time required for acceleration. In this respect, my scheme has somewhat the characteristics of the field frequency scheme.

My scheme, in addition to being of value for starting synchronous motors, is of considerable value in reduced voltage starting for induction motors as it would relieve the auto-transformer of unnecessary load due to incorrect setting of the control time relay.

My scheme also has the advantages of the definite time scheme in that it utilizes the maximum speed to which the damper winding would bring the rotor and in no case will it fail to apply the field in a relatively short time. With this inherent time adjustment found in my starting control, settings for different acceleratin times are not necessary, One setting is made for the most severe condition and for less severe conditions the time is automatically shortened.

To provide a starting control based upon the starting theory I advance, some simple form of revolution counter is necessary. Such a revolution counter should at least havethe following characteristics, it should be simple and positive in its operation, rugged in construction and low in cost, it should automatically come into operation on closing the starting circuit, close a control switch on completion of the number of revolutions for which it is set and then reset itself automatically and instantly.

There are probably a number of ways in which these results may be obtained. In Figs. 2 and 3, I show a simple and rugged device which I believe meets all of the requirements hereinbefore mentioned. For the particular showing I have made of the revolution counter, the sizes of the various gears have been selected on the assumption that av maximum of 200 revolutions is required for the accelerating period, namely, a maximum period of 40 seconds for a 600 R. P. M. This is, of course, only to be taken as illustrative becausewith a motor having a different normal speed, the gear reduction will be different. I

Referring to Fig. 3, the small pinion I00 is mounted on the motor shaft IM and meshes with the larger gear- I02 which drives a gear train that has a total gear ratio of 200:1. Gears I02, I03 and I00 are mounted in a frame I05 which is pivoted at a point I06 midway between the bearings of gears I02, I03 and I04 to 9. Stationary frame I01. Gear I08 has its bearings in th stationary frame. When the revolution counter is not in operation, the spring I09 holds pinion I00 and gear I02 and pinion H0 and gear I08 out of mesh. The revolution counter is provided with a solenoid III or coil which is connected in the electric circuit to be hereinafter described so as to be energized when the starting circuit is established, When this solenoid III is energized, gear I02 is thrown into mesh with pinion I00 and pinion I I0 is thrown in mesh with the gear I08.

On the shaft of gear I08 are mounted two dogs H2 and H3 which can be set at any angular position on the shaft. Mounted above these dogs and secured to the frame I01 are two small mercoid switches which are pivoted so that they may be tilted by dogs H2 and H3, respectively. One of these mercoid switches is arranged in the control circuit to be described to control the energization of the field contactor and the other mercoid switch is arranged to energize a power factor relay when used with the system of control, which energization of the power factor relay takes place through an intermediate relay. The arrangement is such that once the mercoid switch last to operate has operated, the solenoid III is deenergized and in consequence the spring I09 disengages the gear wheels with the result that sprin 41 mounted on the shaft of the gear I08 repositions all of the gears of the revolution counter to their original position so that the revolution counter stands ready to repeat its operation of controlling the starting of whatever motor or system or serve.

control it may be arranged to Fig. 1 is a diagrammatic showing of a system quite schematic.

In the vbottom of Fig. 1, is set by the dog 50 with the result that the field contactor 30 is the power factor relay Operation of the control relay 23 deenergizes the solenoid for the revolution counter which thereupon resets itself to stand ready at any subsequent time to control the starting of the motor M.

A better understanding of my invention can probably be had from a study of a typical starting sequence for a motor. Assuming the attendant wishes to start the motor M and assuming that the direct current buses 56 and 51 button switch 3, stop switch 4, 5 of the low voltage control contactor 6, conduc tor 1 to the bus 8. Operation of the contactor 6 causes the closing of contact members 9 the energized conductor I 0 through conductor 2|, back contact members 22 of the control relay 23, conductor 24, actuating coil 25 of the solenoid Ill, conductor 21 to the energized conductor 1.

opening of the switch by the power factor relay 35.

The instant the motor M starts rotating shaft 31 is rotated, thereby operating the bevelled pintion 01' the actuating coil 25. v

As the motor accelerates, the revolution counter immediately begins to count revolutions and control relay position.

My system of control is also of value for resynchronization. If for any reason the motor pulls out of step, the power factor relay will be caused to operate the switch to thus deenergiz the coil 55 of the field contactor 30 and thus reestablish the discharge circuit for the field winding F and also open the contact members 60.

Opening of the contact members 60 opens the holding circuit for the actuating coil-3B of the control relay 23 with the result that back contact members 22 are closed. Coil thus becomes 'reenergized and the starting cycle is reenacted and the motoris thus brought up to synchronism.

My invention is also of utility in controllingnot only the application of the direct-current excitation to the field winding in response to the operation of a revolution counter but also to control the line voltage supplied to the armature of the motor in response to a revolution counter.

Synchronous motors that are started on low voltage and then transferred to full voltage may either be synchronized before the full voltage is applied or after the full voltage is applied. In the first instance, synchronization takes place before full line voltage is supplied to themotor, whereas in the second case synchronization does not take place until after the motor is supplied with full line voltage. The theory of operation of my invention for controlling the voltage applied to a motor is the same regardless of which order is used. It will be noted, therefore, referring to Fig. 5, that nut 43 which controls the mercoid switch 63 is so positioned on shaft 4| that the actuatiomof the mercoid switch 63 cccurs after the direct current excitation is applied to the field winding F.

In the showing in Fig. 5, the mercoid switch 63 again controls theenergization of the control relay 23 as well as the energization of the voltage coil of the power factor relay 35 but the 23 in the showing in Fig. 5 has the additional function of opening the contact mem bers 83.

To determine the utility of this operation, let us assume that the starting cycle has been carried to the point where the main line switch I3 is energized, namely, to the point where contact members II are closed. Closure of contact members ll establishes a circuit through conductor 10, actuating coil 1| of the contactor 12 to the energized conductor 21. Operation of the contactor 12 causes the closing of contact members 13, 14 and 15, thereby connecting the armature A of the motor M to the buses I, 8 and I1 through the auto-transformers 19, and 8!. Operation of contractor 12 also causes the opening of contact back members 16, 11 and 18 so that the armature is not directly energized from the leads l8, I9 and 20.

When contact members 83 open, as hereinbefore pointed out, the circuit for the actuating coil 1| of contactor 12 is interrupted. As a rebecause it is readily apparent in the art particularlyafter having had the benesame result. I, therefore,

sult, the auto-transformers are disconnected and contact members 16, 11 and 18 close, thereby applying full voltage to the motor M.

In Fig. 6, I show a starting control for an induction motor M. Since there is no field circuit associated with an induction motor, the second mercoid switch from low voltage to high voltage is exactly as shown in Fig. 5 and no further detailed analysis of the operation of the systemshown in Fig. 6 is thought to be necessary. It should be noted, however, in'connection with the various modifications I have shown that these are not exhaustive but are merely given to illustrate my invention, because it'is readily apparent, for instance in Fig. 6, that an additional mercoid switch might be used to control the resistance of the secondary circuit of a wound rotor induction motor.

I do not wish to be limited, therefore,'to the specific showings I have made in this disclosure,

that those skilled fit of the teachings of my invention, can devise other circuit diagrams wish to be limited only by the scope of the claims hereto appended and such prior art as may be pertinent.

I claim as my invention:

1.. In a starting system for an alternating curr 63 is not utilized. The func- -tion of the transfer for accomplishing the rent motor, a source'of alternating current there for having low voltage starting and full-voltage running taps, and means responsive to the number of revolutions of the motor after starting adapted to automatically control the transfer of the motor armature from the low-voltage starting taps to the full-voltage running taps.

2. In a starting system for a synchronous motor having armature windings, a source of alternating current for the motor, ing low-voltage starting taps and full-volts running taps, and control means responsive to a given total number of revolutions of the motor after connection to said low-voltage starting taps adapted to automatically control the transfer of the motor armature windings from the lowit/oltage starting taps to the full-voltage running aps.

3. In a starting control for automatically starting an electric motor, in combination, a synchronous motor having an armature winding and afield winding, means for applying alternating current to the armature winding, a source of direct current, a resistor, a two-position switch arranged so that in one position it connects said resistor across the field winding and in the other position it connects the source of direct current to the field winding, and control means, responsure to a given total number of revolutions the motormakes after the armature is supplied with alternating current, adapted to disconnectsaid resistor from the field winding and to connect the source of direct current to the field winding.

4. In a motor starter, the combination of, a synchronous motor having an armature winding and a field winding, a-source of alternating current, switching means for connecting the armasaid source havture to the source of alternating current, a

a field winding, a source of excitation for the field winding, a switch'for connecting the field winding to said source of excitation, means for energizing the motor :to start the motor, and control means responsive to a given total number of revolutions of the motor, after starting of the motor, adapted to effect the operation of said switch to thus connect the field winding to the source of direct current.

6. In a motor starter, the combination with an alternating current motor having circuits that include starting and running connections, a source of alternating current, switching means for effecting the energization of said motor and for effecting a transfer from the said starting connections to said running connections and control means responsive to the number of revolutions of the motor, after starting of the motor, adapted to effect the operation of said switching means to transfer the motor circuits from the starting connections to the running connections.

7. In a starting system for a synchronous motor, in combination, a synchronous motor, starting connections for the motor, running connections for the motor, a source of alternating current, means for connecting the motor to said source of alternating current whereby said starting connections become energized, and control means, responsive to a given total number of revolutions of the motor, adapted to control the transfer of the motor from the starting connections to the running connections.

8. In a starting system for an alternating current motor, in combination, a motor, starting connections for the motor, running connections for the motor, a source of alternating current, means for connecting the motor to the source of alternating current whereby said starting connections become energized, and means, responsive to a given number of revolutions made by the motor after connection to said source of alternating current, adapted to effect a transfer of the motor connections from the starting connections to the running connections.

9. In a starting system for an alternating current'motor, in combination, a motor, starting connections for the motor, running connections for the motor, a source of alternating current, means for connecting the motor to the source of alternating current whereby said starting connections become energized, means, responsive to a given number of revolutions made by the motor after connection to said source of alternating current, adapted to effect a transfer of the motor connections from the starting connections to the running connections and means for adjusting said last named means to thus effect the transfer at any selected number of revolutions of the motor.'

10. In a starting system for a synchronous motor, in combination, a synchronous motor, starting connections for the motor, running connections for the motor, a source of alternating current, means for connecting the motor to said source of alternating current whereby said start ing connections become energized, control means, responsive to a given total number of revolutions of the motor, adapted to control the transfer of the motor from the starting connections to the running connections, and means for adjusting said control means to thus effect the transfer at any selected total number of revolutions of the motor.

11. In a motor starter, the combination with an alternating current motor having circuits that include starting and running connections, a source of alternating current, switching means for effecting the energization of said motor and for effecting a transfer from the said starting connections to said running connections, control means responsive to the number of revolutions of the motor, after starting of the motor, adapted .to effect the operation of said switching means to transfer the motor circuits from the said starting connections to the said running connections and means for adjusting said control means for any selected number of motor revolutions.

12. In a motor starting system of the type described, the combination with a motor having a field winding, a source of excitation for the field winding, a switch for connecting the field winding to said source of excitation, means for energizing the motor to start the motor, control means responsive to a given total number of revolutions of the motor, after starting of the motor, adapted to effect the operation of said switch to thus connect the field winding to the source of direct current, and means for adjusting the control means to thus be responsive to any given number of total motor revolutions.

13. In a motor starter, the combination of, a synchronous motor having an armature winding and a field winding, a source of alternating current, switching means for connecting the armature to the source of alternating current, a source of direct current, switching means for connecting the field winding to the source of direct current and control means, including a revolution counter set in operation the instant the source of alternating current is connected to the armature, adapted to cause the operation of the last named switching means when the motor has -made a given total number of revolutions after the operation of the first named switching means and means for adjusting the revolution counter for different selected total number of revolutions.

14. In a starting control for automatically starting an electric motor, in combination, a synchronous motor having an armature winding and a field winding, means for applying alternating current to the armature winding, a source of direct current, a resistor, a two-position switch arranged so that in one position it connects said resistor across the field winding and in the other position it connects the source of direct current to the field winding. control means, responsive to a given total number of revolutions the motor makes after the armature is supplied with alternating current, adapted to disconnect said resistor from the field winding and to connect the source of direct current to the field winding, and means for adjusting the operating characteristics of said control means so that said control means is made responsive to any selected total number of revolutions the motor makes after energization with alternating current.

15. In a starting system for a synchronous motor having armature windings and field windings, a source of alternating current for the motor, said source having low-voltag starting taps and full-voltage running taps, a source of. direct current, said field winding having a starting, or discharge circuit, connection and a running connection, field switching means adapted to transfer the field winding from the starting 4 i i l e or discharge circuit connection to the running connection to be energized with direct current from said source of direct current, and control means responsive to a given total number of revolutions of the motor after connection to said low-voltage, starting taps adapted to automatically control the transfer of the motor armature windings from the low-voltage starting taps to the full-voltage running taps, means responsive to a given total number of revolutions of the motor after connection to said low-voltage taps adapted to automatically effect operation of the field switching means to transfer the field winding connection from the discharge circuit connection to the connection energizing the field with direct current.

16. In a starting system for a synchronous motor having armature windings and field windings, a source of alternating current for the motor, said source having low-voltage starting taps and full-voltage running taps, a source of direct current, said field winding having a starting, or discharge circuit, connection and a running connection, field switching means adapted to transfer the field winding from the starting or discharge circuit connection to the running connection to be energized with direct current from said source of direct current, and control means responsive to a given total number of revolutions of the motor after connection to said low-voltage starting taps adapted to automatically control the transfer of the motor armature windings from the low-voltage starting taps to the full-voltage running taps,'means responsive'to a given total number of revolutions of the motor after connection to said low-voltage 'taps adapted to automatically effect operation of the field switching means to transfer the field winding connection from the discharge circuit connection to the connection energizing the field after connection to said. low-voltage starting taps adapted to automatically control the transfer 01' the motorr armature windings from the lowvoltage starting taps to the full-voltage running taps, and means for-adjusting the control means to thus be responsive to any selected total number of motor revolutions.

18. In a starting'system for an alternating current motor, a source of alternating current therefor having low-voltage starting and fullvoltage running taps, means responsive to the number of revolutions of the motor after starting adaptedto automatically control the transfer of the motor armature from the low-voltage starting taps to the full-voltage running taps and means for adjusting said means responsive to the number of revolutions of the motor to make it responsive to any selected number of revolutions of the motor.

19. In a system for starting an alternating current motor, in combination, an alternating current motor, means for energizing the motor to start it, starting circuits for the motor adapted to become energized the instant the motor is energized for starting, a revolution counter adapted to become operative to count motor revolutions the instant the motor is started, running circuits for the motor, and control means responsive to a selected number of revolutions counted by the revolution counter adapted to energize the running circuits for the motor and to deenergize the starting circuits for the motor.

20. In a system for starting an alternating current motor, in combination, an alternating current motor, means for energizing the motor to start it, starting circuits for the motor adapted to become energized the instant the motor is energized for starting, a revolution counter adapted to become o erative to count motor. revolutions the instant the motor is started, running circuits for the motor, control means responsive to a selected number of revolutions counted by the revolution counter adapted to energize the running circuits for the motor and 

